I have booked a cruise on P and O Oceana for myself and my girlfriend, we have never been on a cruise before but decided to go for it as the ship visits destinations we are interested in seeing and we got a very good deal. I am a bit worried about a few things: firstly we are quite young both 24 (but quite mature for our age in the fact that we don't like the typical Ibiza 18-30 hoilday most people our age go on) and are a bit worried we will be out of place. We are also a bit worried about how formal the dress has to be I have a dark suite but do you have to wear a tux? or a bow tie? And advice would be great, we leave in 5 days are really looking forward to it.

Chris, your suit will be just fine and a regular tie will work. Tux's only are worn by a small percentage of the passengers on most ships anymore. In fact, my husband got rid of his as he said a suit is much more comfortable when he is 'on vacation'.
Just remember that a cruise is what YOU want it to be. It can get very hectic if you want, or it can be the most relaxing vacation you have ever had. It's YOUR call and you do exactly what makes you happy, nothing rigid and take each moment as it comes.
Sometimes the ones that plan every second of their cruise out ahead of time are the ones that may get a little disappointed in the experience. There is so much to do, or not to do, but it is all your decision.
Hope you enjoy your first cruising experience!!!!